Process for removing bismuth from copper or copper-containing melts and products



Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE AND PRODUCTS Otto Nielsen, Ilsenburg/Harz, Germany, and Erwin Richard Lauber, Rorschach, Switzerland; said Lauber assignor to said Nielsen No Drawing.

. rial No. 55,296.

12 Claims.

This invention relates to a process for removing bismuth from copper or from melts and prod,- ucts containing it,

In the processes heretofore known for the working up of copper ores, previously subjected if desired, to a. dressing process, in general three stages are distinguished, vizzi'irstly, the matte fusion stage, carried out in most cases in flame or reverberatory furnaces; secondly, the blasting of the copper matte in a converter, andthirdly, the refining of the blister copper thus obtained.

In processes of this kind the bismuth content is reduced it is true, but not to such an extent that, especially if the crude product contains a. large percentage of bismuth, a copper is obtained which is so poor in bismuth that it is utilisable for further working.

It is also known that during the blasting of the copper matte in the converter the relatively greatest part of the bismuth is removed as well, but this takes place in uncontrollable quantities which vary from charge to charge.

Bismuth, as is well known, is one of the most feared impurities in copper, as a bismuth content of even only a few thousandths of one per cent exerts an unfavorable influence upon the mechanical properties of the copper, and contents of more than M percent render the copper useless for most purposes.

The present invention consists in carrying out the metallurgical process in all its stages in such a manner that a final product is obtained which is practically free from bismuth, that is to say, contains about less than 0.002%. According to this invention the bismuth is removed by treating the melt with silicic acid or silica or substances containing the same during the metallurgical process.

It has been discovered that the removal or evaporation of bismuth'takes place not directly, but by way of intermediatelyfformed bismuth silicates or mixtures of silicates. For instance, when a copper matte containing a very large percentage of bismuthwas heated to high temperatures in the "absence of silicate no substantial quantities of bismuth were removed.

It is known, it is true, to add silicic acid and silicates in the blasting of copper'matte in order to flux or slag the iron. These additions are e'ffected by throwing them on the surface of the converter bath, during the tilting or during'the blasting phase under pressure. In the usual practice of blasting copper in a. converter silicic acid is added in order to produce a slag which is sufflciently liquid tube run out of the converter.

Application December 19, 1935, Se-

In Germany December -21,

Since the slag which is formed in this way is so rich in copper that it is subjected yet again to a fusion process it is usual to keep the silicic acid addition no larger than is absolutely necessary to impart to the slag that degree of liquidity which is sufficient, since every further addition of silicic acid unnecessarily enlarges the quantity of slag to be further treated.

According to the present invention, on the other hand, the metallurgical process is carried out in its individual stages with a quantity of silicic acid which is always sufllcient to produce a removal of the bismuth which is as extensive as possible. By an excess of silicic acid is thereby 4 to be understood a quantity such that not onlysilicic acid be present in sufficient quantity, since it is well known that it is mainly in this stage that the said oxygen compounds, which prevent a subsequent suflicient removal of the bismuth, are formed.

Once such. oxygen compounds have been formed, it is no longer possible to attain sufficient removal of the bismuth even by a subsequent copious addition of silicic acid. A slag in its ends state, for example, may therefore show a higher silicic acid content without the bismuth having been removed, in contra-distinction to the slag from another charge with a smaller silicic acid content. In the former case the condition of having a sufllcient quantity of silicic acid present at the beginning or in the various stages of the process has not been observed.

The silicic acid is used in a state in which it is as reactive as possible, and in fact as finely ground as possible. silicates which have been decomposed by sulphuric acid can also be employed. The addition of the silicic acid may also take place with an addition of small amounts of alkali chlorides or alkali sulphates. The addition of silicic acid or of additions containing the same should be effected as uniformly as possible and the fused mass should uniformly come in contact with the same as well.

The minimum amount of silicic acid also depends, therefore, apart from the amount of bismuth to be removed, upon the working conditions chosen and also upon the quality or condition and reactivity of the silicic acid itself. The amount, therefore, must be chosen at least so large that 5 the bismuth is actually removed to an extent sufficient for the purpose in view.

It is furthermore known that metallic copper takes up bismuth eagerly, and that after the formation of metallic copper hardly any diminulo tion of the bismuth content is possible in the known methods of further working the copper (see "Metallurgy of Copper, Hofmann-Hayward, 2nd edition, page 227, Selective Converting). According to this invention, therefore, the volatilisation of the bismuth is carried out, at least 7 for its greatest possible portion, within the time that no metallic copper is yet present during the metallurgical process.- The formation of copper takes place in the course of the converter process when the composition of the matte corresponds to the formula CuzS. .If, however, the entire contents of the converter are not homogeneous, the formation of metallic copper begins earlier at certain points thereof. This will always be the case in practical operations, especially if attempts are made, by the employment of a reduced amount of blast, to extend the time of existence for the stage of a copper content of less than 79.8%. According to the present improved process it is further possible, as described below, to extend this time without unhomogeneous compositions being able to arise which unfavorably influence the degree of efiiciency of the removal of the bismuth, the present process being t0 a certain extent independent of the copper content of the matte. v

The improved process according to this invention is carried out for example as follows:.

According to the starting material used, especially as regards the bismuth content of the same, operations will be carried out with an addition'of silicic acid even during the fusion of a matte. By working with slag containing a large amount of silicic acid when fusing the matte a reduction in the bismuth content already occurs. The removal of the greater part of the bismuth contamination however, is preferably effected during the converter process.- acid, or additions containing it, are added as uniformly as possible, preferably by blowing in with the blast through the blow nozzles. It is also of advantage to avoid adding oxidicsubstances during the converter process, such as oxldic ore, converter slag and refining slags.

In order to avoid a premature formation of metallic copper, the rate of reaction and the temperature are suitably regulated. This may be effected, for instance, by addition of carbon or coal, preferably mixed with silicic acid, and 00 by introducing the same through the blow nozzles by means of the blast.

The current of air must always be sufiicientiy strong to be able thoroughly to whirl up the contents of the converter. If this is effected solely l 05 by the blowing in of air, as is usual, then the amount of copper in the contents of the converter rises more quickly than is desirable for the vaporisation of thebismuth. Owing to carbon in any desired form being blownin with the 70 blast, the gas current consists then chiefly of the carbon oxides and nitrogen. If the addition of carbon is so large as to consume the entire oxygen of the air, or if oxygen-poor air, e. g. flue gas, is used, then the copper content can be 7 maintained at the same percentage, so that the Silicic ishing blowing of the melt to copper, by further additions of silicic acid.

As has already been mentioned, heretofore it has not been possible appreciably to reduce the bismuth content once the bismuth was present in the metallic copper. According to the present invention, however, it is possible still further to reduce the bismuth content even in the refining process with the aid of an addition of silicic acid. It is, in this case, of advantage to add lead to the blist'er copper. When in the refining phase the charge has then taken up sufiicient oxygen, an addition of silicic acid and other fluxes such as sodium sulphate and/or sodium chloride is blown in. A part of the bismuth then passes over into the resulting slag 'whilst another part vapor'ises. The lead content need not a in itself be large; it may amount to about 0.1%. Also in the copper matte a lead content increases the efilciency of the process in the converter phase.

According to a further modification of the invention ferrosilicon is used partly or wholly in place of the silicic acid. As equivalent to additions of ferrosilicon are to be regarded all additions of substances or mixtures of substances which are capable of bringing about an intermediate formation of ferrosilicon in the fusion vessels themselves. For example, a mixture of silicic acid and carbon (or coal) in the presence of.iron yields ferrosilicon at comparatively low temperatures.

The process provided by the invention can of course, as described, be extended to all stages of the usual metallurgical processes.

It is also possible to transfer it in an appropriate manner to other procedures, or to introduce its use only partly, or to use it solely more particularly in connection with the blast phase.

In the case of a high bismuth content in the starting material, it will, of course, always be of advantage to carry out all stages of theprocess in the described manner.

What we claim is:

1. In the extraction of copper from its ores and compounds by the blast converter process, the

step of adding to the copper-containing material substantially throughout the blasting a silicate which has been decomposed by treatment with sulphuric acid, the amount of decomposed silicate added being sufflcient not only to slag the impurities, e. g. iron, but to remove the bismuth as well. I

2. In the extraction of copper from its ores and compounds by the blast converter process, the step of adding silicic acid to the blister copper during the blasting for the purpose of ensuring the removal of bismuth from the latter.

3. In the process defined in claim 2 the step of adding a small quantity of lead also to the blistercopper.

4. In the extraction ofcopper from its ores and compounds by the blast converter process, the step of adding a sufficient amount of widely distributed and finely divided silicic acid at the start of the blasting, to the copper-containing material, to maintain at all times admixed with the charge, a quantity of said silicic acid sufllcient not only to slag the impurities, e. g. iron, but to remove the bismuth as well.

5. In the process defined in claim 4, the feature of preventing a formation of injurious oxidic compounds, such as ferrites, as far as possible by maintaining an excess of the silicic acid during the process.

6. In the process defined in claim 4, the feature of preventing premature reduction of copper at some portions of the charge, by maintaining the copper-containing material homogeneous by agitation thereof by the blast during the period in which the removal of the bismuth takes place.

7. In the process defined in claim 4, the feature of deviating from standard practice by maintaining the material free from any addition of injurious oxidic material, of the group consisting of oxidic ores, converter slags, and refinery slags.

8. In the extraction of copper from its ores and compounds by the blast converter process, the step of adding silicic acid and carbon material to the copper-containing material at the start and also at intervals during the progress of the process, the amount of silicic acid added being sufficient not only to slag the impurities, e. g. iron, but also to remove the bismuth, the amount of carbon added being sumcient to delay the formation of the higher oxides of iron until after the bismuth has been removed.

9. A process as=defined in claim 8 in which the silicic acid and carbon material are used in admixture with each other.

10. In the extraction of copper from its ores and compounds by the blast converter process, the step of introducing silicic acid into the converter charge by blowing it in with the blast, at the start and also substantially throughout the duration of the blowing treatment, the amount introduced being sufllcient not only to slag the impurities, e. g. iron, but also to remove the bismuth.

11. In the extraction of copper from its ores and compounds by the blast converter process, the step of introducing silicic acid and carbon material into the converter charge by blowing the same in with the blast, at the start and also substantially throughout the blasting, the amount of silicic acid introduced being sufficient not only to slag the impurities, e. g. iron, but also to remove the bismuth, and the amount of carbon added being suflicient to delay the formation of the higher oxidesof iron until after the bismuth has been removed.

12. In the process defined in claim 4 the step containing material.

o'rro NIELSEN. ERWIN RICHARD LAUBER. 

